1. Field of the Invention
This invention relates generally to airless spray nozzles, and more particularly relates to airless spray nozzles used in the coating industry.
2. Description of the Prior Art
Spray nozzles are used to break up a liquid into a large number of small droplets. This process is called atomization. The atomization of liquids is used for varied purposes such as applying insecticides to plants, spraying water, and applying coating material to a substrate. Upon discharge from the atomizing nozzle, the fluid breaks up into droplets and forms a spray pattern or a cloud of droplets. In the spray coating industry, a common pattern is in the shape of a flat fan. The flat fan may have paint droplets concentrated heavily in the middle with a diminishing amount of paint droplets in the fan as the edges of the fan are approached; or, paint droplets may be heavily concentrated at one side with a diminishing amount as the other side of the fan is approached.
Nozzles to produce flat fan patterns generally take one of two forms: either air or airless. Air atomizing nozzles issue a stream of fluid which is broken up by jets of air directed at the fluid issuing from the nozzle. Airless spray nozzles effect the breakup of the fluid by causing the fluid to be ejected in a thin film or sheet. Forces acting on this sheet of fluid cause it to break up into small droplets. The physical mechanisms causing the sheet to break up into droplets is well known in the art and will not be discussed in detail here.
Many different approaches have been taken to construct airless spray nozzles. Invariably, the airless spray nozzle tips comprised a blank or member from which the tip would be made in which an opening or orifice had been formed. The orifice was generally formed by the interpenetration of two recesses; one recess from either side of the tip. The shape of the recesses have been many and varied. The most widely used airless spray nozzle tips today utilize a domed shape recess on the pressurized side of the tip with an interpenetrating recess from the other side of the tip.
It is desirable to make the nozzle tip out of a very hard material such as ceramic or sintered tungsten carbide. The hard material decreases the rate at which the nozzle orifice will wear. In airless nozzle tips made from these materials, at least one of the recesses (for example, the dome) was formed in the material before final hardening.
Another approach to making a nozzle tip orifice is described in the U.S. Pat. No. 1,151,258 issued to Fischer. In this patent the nozzle tip is formed by interpenetrating cuts from either side of the tip. The cuts are made by cutting wheels which have small rotating or spinning radii and therefore produce curved bottom slots in either side of a disc-like tip member. This nozzle was used to produce a fan shaped spray pattern for an oil burner.